Avoid uninitialized result in sem_open when file does not exist

[Adhemerval Zanella Netto]

On 07/11/24 21:29, Joseph Myers wrote:
> A static analyzer apparently reported an uninitialized use of the
> variable result in sem_open in the case where the file is required to
> exist but does not exist.
> 
> The report appears to be correct; set result to SEM_FAILED in that
> case, and add a test for it.
> 
> Note: the test passes for me even without the sem_open fix, I guess
> because result happens to get value SEM_FAILED (i.e. 0) when
> uninitialized.
> 
> Tested for x86_64.
> 
> diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
> index 4c1dc04b20..7f52e7d511 100644
> --- a/sysdeps/pthread/Makefile
> +++ b/sysdeps/pthread/Makefile
> @@ -256,6 +256,7 @@ tests += \
>    tst-sem14 \
>    tst-sem15 \
>    tst-sem16 \
> +  tst-sem17 \
>    tst-setuid3 \
>    tst-signal1 \
>    tst-signal2 \

We already have a tst-sem17 on nptl, maybe rename it to tst-sem18.

> diff --git a/sysdeps/pthread/sem_open.c b/sysdeps/pthread/sem_open.c
> index e41236157a..dab734191a 100644
> --- a/sysdeps/pthread/sem_open.c
> +++ b/sysdeps/pthread/sem_open.c
> @@ -76,6 +76,7 @@ __sem_open (const char *name, int oflag, ...)
>  	    goto try_create;
>  
>  	  /* Return.  errno is already set.  */
> +	  result = SEM_FAILED;
>  	}
>        else
>  	/* Check whether we already have this semaphore mapped and
> diff --git a/sysdeps/pthread/tst-sem17.c b/sysdeps/pthread/tst-sem17.c
> new file mode 100644
> index 0000000000..c3f05d196f
> --- /dev/null
> +++ b/sysdeps/pthread/tst-sem17.c
> @@ -0,0 +1,35 @@
> +/* Test sem_open with missing file.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <semaphore.h>
> +
> +#include <support/check.h>
> +
> +int
> +do_test (void)
> +{
> +  sem_unlink ("/glibc-tst-sem17");
> +  errno = 0;
> +  sem_t *s = sem_open ("/glibc-tst-sem17", 0);
> +  TEST_VERIFY (s == SEM_FAILED);
> +  TEST_COMPARE (errno, ENOENT);
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
>